The use of polyalpha-olefins or copolymers thereof to reduce the drag of a hydrocarbon flowing through a conduit, and hence the energy requirements for such fluid hydrocarbon transportation, is well known. These drag reducing agents or DRAs have taken various forms in the past, including slurries or dispersions of ground polymers to form free-flowing and pumpable mixtures in liquid media. A problem generally experienced with simply grinding the polyalpha-olefins (PAOs) is that the particles will “cold flow” or stick together after the passage of time, thus making it impossible to place the PAO in the hydrocarbon where drag is to be reduced, in a form of suitable surface area, and thus particle size, that will dissolve or otherwise mix with the hydrocarbon in an efficient manner. Further, the grinding process or mechanical work employed in size reduction tends to degrade the polymer, thereby reducing the drag reduction efficiency of the polymer.
One common solution to preventing cold flow is to coat the ground polymer particles with an anti-agglomerating or partitioning agent. Cryogenic grinding of the polymers to produce the particles prior to or simultaneously with coating with an anti-agglomerating agent has also been used. However, some powdered or particulate DRA slurries require special equipment for preparation, storage and injection into a conduit to ensure that the DRA is completely dissolved in the hydrocarbon stream. The formulation science that provides a dispersion of suitable stability such that it will remain in a pumpable form necessitates this special equipment.
Gel or solution DRAs (those polymers essentially being in a viscous solution with hydrocarbon solvent) have also been tried in the past. However, these drag reducing gels also demand specialized injection equipment, as well as pressurized delivery systems. The gels or the solution DRAs are stable and have a defined set of conditions that have to be met by mechanical equipment to pump them, including, but not necessarily limited to viscosity, vapor pressure, undesirable degradation due to shear, etc. The gel or solution DRAs are also limited to about 10% polymer as a maximum concentration in a carrier fluid due to the high solution viscosity of these DRAs. Thus, transportation costs of present DRAs are considerable, since up to about 90% of the volume being transported and handled is inert material.
U.S. Pat. No. 2,879,173 describes a process for preparing free-flowing pellets of polychloroprene involving suspending drops of an aqueous dispersion of the polychloroprene in a volatile, water-immiscible organic liquid in which the polymer is insoluble at temperatures below −20° C. until the drops are completely frozen and the polychloroprene coagulated, separating the frozen pellets from the suspending liquid, coating them while still frozen with from 5% to 20% of their dry weight of a powder which does not react with the polychloroprene under normal atmospheric conditions, and removing the water and any adhering organic liquid through vaporization by warming the pellets.
A method for coating pellets of a normally sticky thermoplastic binder material by using a mixture of a minor proportion of a vinyl chloride/vinyl acetate copolymer and a major proportion of a chlorinated paraffin wax with powdered limestone or talc powder is described in U.S. Pat. No. 3,351,601.
U.S. Pat. No. 3,528,841 describes the use of microfine polyolefin powders as parting agents to reduce the tackiness of polymer pellets, particularly vinyl acetate polymers and vinyl acetate copolymers.
Similarly, Canadian patent 675,522 involves a process of comminuting elastomeric material for the production of small particles that includes presenting a large piece of elastomeric material to a comminuting device, feeding powdered resinous polyolefin into the device, comminuting the elastomeric material in the presence of the powdered polyolefin and recovering substantially free-flowing comminuted elastomeric material.
A process for reducing oxidative degradation and cold flow of polymer crumb by immersing the crumb in a non-solvent such as water and/or dusting the crumb with a powder such as calcium carbonate and 2,6-di-t-butylparacresol, 4,4′-methylene-bis-(2,6-di-t-butylphenol) or other antioxidants is discussed in U.S. Pat. No. 3,884,252. The patent also mentions a process for reducing fluid flow friction loss in pipeline transmission of a hydrocarbon fluid by providing a continuous source of the dissolved polymer.
U.S. Pat. No. 4,016,894 discloses that drag in turbulent aqueous streams is reduced by a powder composition of a finely divided hygroscopic drag reducing powder, for example poly(ethylene oxide), and a colloidal size hydrophobic powder, for example, an organo silicon modified colloidal silica, and an inert filler such as sodium sulfate. The powder composition is injected into the turbulent stream by first mixing the powder with water to form a slurry and immediately thereafter drawing the slurry through an eductor into a recycle stream between the downstream and upstream ends of a pump for the turbulent stream.
A polymer emulsification process comprising intimately dispersing a liquified water insoluble polymer phase in an aqueous liquid medium phase containing at least one nonionic, anionic or cationic oil-in-water functioning emulsifying agent, in the presence of a compound selected from the group consisting of those hydrocarbons and hydrocarbyl alcohols, ethers, alcohol esters, amines, halides and carboxylic acid esters which are inert, non-volatile, water insoluble, liquid and contain a terminal aliphatic hydrocarbyl group of at least about 8 carbon atoms, and mixtures thereof are described in U.S. Pat. No. 4,177,177. The resulting crude emulsion is subjected to the action of comminuting forces sufficient to enable the production of an aqueous emulsion containing polymer particles averaging less than about 0.5 microns in size.
U.S. Pat. No. 4,263,926 provides a method and apparatus for maintaining polymer particles in readily recoverable, discrete form, and for injecting the particles into a pipeline hydrocarbon by disposing particulate polymer within a storage hopper having a cone bottom and an auger extending upwardly from the bottom. The auger is rotated to cause the polymer particles to revolve in the hopper, reversing the rotation of the auger to pass polymer particles downwardly into a mixing chamber below the hopper. The particles pass through a rotary metering valve, or optionally, a bin activator, intermediate storage and rotary metering valve at the upper end of the chamber, simultaneously spraying a liquid such as oil or water tangentially in the chamber optionally agitating the chamber and removing a slurry of particulate polymer and liquid from the chamber and injecting the slurry into a pipeline hydrocarbon.
A technique for extremely rapid dissolution or dispersion on essentially the molecular level, of certain polymeric materials in compatible liquid vehicles is described in U.S. Pat. No. 4,340,076. The polymeric materials are comminuted at cryogenic temperatures and are then introduced into a liquid vehicle preferably while still at or near cryogenic temperatures. At low concentrations, the resulting blend or system displays reduced friction to flow while high concentrations may be used to immobilize the liquid vehicle and/or reduce its vapor pressure.
From reviewing the many foregoing prior patents it can be appreciated that considerable resources have been spent on both chemical and physical techniques for easily and effectively delivering drag reducing agents to the fluid that will have its drag or friction reduced. Yet none of these prior methods has proven entirely satisfactory. Thus, it would be desirable if a drag reducing agent could be developed which rapidly dissolves in the flowing hydrocarbon (or other fluid), which could minimize or eliminate the need for special equipment for preparation and incorporation into the hydrocarbon, and which could be formulated to contain greater than 10% polymer. It would also be desirable to have a process for producing particulate drag reducing agents that did not require cryogenic grinding in its preparation and/or only grinding under ambient temperature conditions.
Another important consideration in the production of polymeric drag reducing agents is the achieving of high conversions in the polymerization reaction, which are defined herein as generally on the order of at least 90%. High conversion makes the best use of the monomer and catalysts and achieves a high molecular weight polymer product. The high molecular weight polymer product helps mitigate subsequent degradation of the polymer product through size reduction, such as granulation or grinding, as well as through shear when the DRA product passes through pumps in the course of injecting it into a flowing hydrocarbon fluid or through a pipeline. Conventionally, high conversions and high molecular weights of DRA polyolefins are achieved by bulk or neat polymerizations conducted in batch reactions. However, it is well known in the art of polymerization science that the most efficient method of producing polymers en masse is through the methods of continuous polymerization processes. Thus, the preferred production processes of high volumes of DRA product are continuous processes. Some prior efforts at the continuous production of DRA product by employing bulk polymerization methods have been explored but have not proven entirely satisfactory either. One innovative approach is to conduct bulk polymerization at high conversion in a microcapsule described in U.S. Pat. Nos. 6,126,872 and 6,160,036, both of which are incorporated by reference herein.
It would thus be additionally advantageous if a continuous process existed for producing DRA polymer product at high conversions and molecular weight, yet in a form that was easily deliverable to a flowing hydrocarbon stream.